Slump and slump flow for characterizing yield stress of fresh concrete

Rheological properties of fresh concrete, namely yield stress and plastic viscosity, can be used to differentiate concrete mixtures for the purpose of controlling their quality. Different types of concrete rheometers have been developed to measure the rheological properties; however, it is found that the measured absolute values vary significantly among the various apparatuses. Further, it has been recognized that the slump measurement, a simple and universal test method in comparison to concrete rheometers, can be used to characterize the yield stress. This study examines various analytical and empirical models that have been proposed in the literature for quantifying the yield stress on the basis of slump and slump flow measurements. Experimental data, which have been reported in the literature, are used to assess the applicability of these models. The results show that the slump versus slump flow relationship proposed by Chidiac and coworkers agrees well with the published experimental data. With the exception of the rheological model proposed by Chidiac, which employs a slump flow measurement, the others provide an estimate for the yield stress using the slump measurement alone. Results reveal that most analytical and empirical model predictions of the yield stress are in good agreement with test results, and that the prediction of the yield stress using the slump flow measurement has the best correlation with respect to the experimental data. Copyright © 2006, American Concrete Institute. All rights reserved.